PolyAdenylation using polyA polymerase

We need HELP!
For some time now we polyadenylate in vitro transcripted and purified mRNAs with polyA polymerase from USB, but all of a sudden it stopped working.
We tried different polymerases, different templates and different ATPs. We also tried different purification methods before polyadenylation (3 Kits, LiCl and nothing at all).
Does anyone have an idea what else we could change so it works again?
Thank you soooo much.
Schnuffel